Saturday 10 December 2011 05.00 EST
First published on Saturday 10 December 2011 05.00 EST

After seeing his rivals for the GOP presidential nomination self-destruct one by one, tonight's debate in Iowa offers Mitt Romney his best opportunity to arrest Newt Gingrich's sudden surge in popularity.

As poll after poll in recent days has shown that Gingrich has replaced Romney as undisputed frontrunner for the Republican nomination, Romney's campaign has been forced onto the offensive – a policy that Romney will have to continue in tonight's debate in Des Moines.

Romney previewed the tactics he is likely to use against the former Speaker of the House on Friday, poking fun at a series of Gingrich's more fanciful ideas, including a permanent moon base and paying children from improverished families to clean school bathrooms.

Meanwhile, prominent Romney supporters lashed out at Gingrich in harsher terms, calling him unstable and untrustworthy, and a brutal new ad attacking Gingrich as a flipflopper who would lose in the general election to Obama has been released by a political action committee that backs Romney through a site called newtfacts.com.

Gingrich was quick to reply in kind on Friday with a stinging claim that Romney's 1994 Senate bid saw him campaign "to the left of Ted Kennedy," thus tying Romney to the Massachusetts liberal icon.For months Romney has remained above the fray, generally avoiding interviews and using his debate appearances to focus on Obama. In the dozen previous debates Romney and Gingrich have circled each other wearily, but Gingrich's slender poll ratings earlier in the contest meant Romney wasted little energy in attacking him.

Those long stretches of front-runner status, as challenges from Tim Pawlenty, Michele Bachmann, Perry and Herman Cain all came and went, now seem like wasted opportunity for Romney, as his solid if underwhelming polling position in the key early primary states has been eroded by Gingrich.

Gingrich's rise has been on the back of his pugnacious debate performances, in which the media as well as the Obama administration has been his target.

But Romney has shown himself to be a tenacious, disciplined debater – and his clipped manner could see him match Gingrich's sniping. Earlier debates saw Romney prepared to trade verbal blows with Texas governor Rick Perry – and with Perry folding under the glare of the debate spotlight.

Aside from Romney versus Gingrich, the other five candidates on stage will be lining up to take a swing at the front-runners in an effort to boost their own chances with a little more than three weeks remaining until the Iowa caucuses.

Reports from Iowa and strong recent polling suggest that Ron Paul, a libertarian-leaning veteran candidates, could cause an upset by winning the caucuses thanks to a groundswell of support and a vibrant campaign in the Hawkeye state.

Paul's threat could see him attract more hostility from his rivals on stage, who are likely to take aim at his opposition to US military involvement abroad.

Tonight's debate starts at 9pm ET from Drake University in Des Moines, jointly hosted by ABC News, the Des Moines Register and Yahoo. The Guardian will be live-blogging the debate with contributions from correspondents in Washington DC and Des Moines.